An annoying person, usually male, characterized by one or more of a variety of obnoxious traits. These may include but are not limited to arrogance, incompetence, stupidity, an unfounded sense of self-importance, and general disagreeableness. See douchebag.
Mack: Well sonofabitch, here comes that bumbling idiot Todd who thinks he's God's greatest gift to humankind.
Jensen: He's coming this way? Ah fuck. What a royal douche canoe.
Not a definition but the orgin of the phrase: This phrase was coined in 2004 by Blake Edmondson in Camp Walker, South Korea. It was used as an alternative phrase for someone being a complete moron / dick / dirtbag. After Edmondson transferred stations I attempted to pass this phrase on along with other greats such as..... Gungle a gungle, (rumble of a V8) Kadouche (boom), and Splack (disgusting splash).